OBJECTIVES: (1) The study of the slow transient in the progress curves of transketolase will be continued, to investigate whether competitive inhibitors act by interfering with the rate-limiting dimerization to give active holoenzyme, or simply compete in the catalytic step. this will be done by assessing the lag and the steady state velocity, and also by sedimentation studies. (2) Pyruvate decarboxylase will be studied at various pH to determine whether oligomerization becomes rate-limiting under any circumstances. The effect of competitive inhibitors on the length of the lag and on the catalytic process will be investigated, to determine at what point those inhibitors act. (3) Spin-echo NMR studies will be undertaken to assess the nature of the enzyme-substrate-M2 ion-coenzyme interactions in transketolase. (4) Attempts will be continued to synthesize ethenothiaminpyrophosphate. The parent substance, ethenothiamin, is highly fluorescent, and the pyrophosphate will be a useful probe of the active sites of thiamin-PP requiring enzymes.